Can i add new circuits onto installation with undersized main bonding?

[goldie]

Can i add new circuits to a system (rcd protected ofcourse) with under sized main protective bonding, without having to upgrade to 10mm2?
E.G tn-c-s earthing system with 6mm2 protective bonds but should be 10mm2 as neutral is less than 35mm2, This could be a code 4 on a pir or code 3 on a ecr which would not fail the inspection, but do i still have to make sure that the bonding is brought up to date?

 

[Deleted member 26818]

My opinion, is that yes you can.
The requirement is to ensure the earthing and bonding arrangements are adequate (if required) for the safety of the protective measure you are going to install.
To my mind, bonding will not affect the operation of the RCD.

 

[telectrix]

i assume you're talking of bonding to gas/water. if 6mm is adequate ( 50% of calculated minimum for main earthing conductor ) then it's OK.

 

[goldie]

i assume you're talking of bonding to gas/water. if 6mm is adequate ( 50% of calculated minimum for main earthing conductor ) then it's OK.

Exept where pme condition apply, It would then have to be 10mm2 if supply neutral is 35mm2 or less. Reg 544 i think? Dont think 6mm is adequate so want to make sure i dont carry out work until bonding is satisfactory, but also dont want to look asthough im ripping customer off by charging for un neccesary upgrade of bonding.

 

[telectrix]

OK. measure your pefc. trhen use adiabatic to determine the min. size of main earthing for that pefc and the appropriate disconnection time of the DNO fuse. if that result is 12mm or less ( which it will be unless you have a very high pefc) then 6mm for bonding (50%) is adequate.

 

[claret73]

If I read it right, he's stated TN-C-S, therefore PME requires 10mm Protective Bonds if Neutral less than 35mmsq. Pg 134 Table 54.8 Reg 544.1.1

 

[goldie]

Yep makes sense to me, Thanks guys regs seem contradicting at times, Think i can jst about remember (I2 t)k etc??

 

[claret73]

I'm not aiming to prove incorrect, I'd happily be told I am myself. Times on here I look at things & go away & find out myself, so this is one of them. Where's the Contradiction??? TN-C-S 16mm Earth, 10mm Bonds...Adiabatic is used on TN-S

 

[goldie]

If I read it right, he's stated TN-C-S, therefore PME requires 10mm Protective Bonds if Neutral less than 35mmsq. Pg 134 Table 54.8 Reg 544.1.1

so do i use my adiabatic equation or go with this regulation (this is why regs contradict in my opinion)

 

[claret73]

Goldie...Please don;t get me confused!!!! LOL...Adiabatic is for determining the Earthing Conductor by which Bonding conductors can be selected. Except...PME given by the Reg above...That's my take. Your 6mm is too low due to TN-C-S Earthing arrangement at current Regs. You can show the BRB Page info to your Client I guess...

 

[goldie]

Thanks claret. But am i allowed to commence work on this installation by adding circuit? see my first post then give me an answer please mate, so i can go to bed........... my head hurts

 

[Deleted member 26818]

Yes where PME conditions apply, both the earthing conductor and the protective bonding conductors have to be a minimum of 10mm².
However, bonding is not required for ADS or for RCDs to operate, as such there is no requirement to upgrade the bonding.

 

[claret73]

Mate
I know how you feel!!!! My Head don't half hurt at times & fully agree the Regs are contradictory at best of times, but my opinion (& it's only that) is that I've given you correct info here. I don't do my own Notifiable work as I sub to Contractors but I'm sure it goes along the lines that prior to commencing you need to ascertain correct installation of Bonding Conductors - try the Part P doc? I'll take a look myself...Get some shut eye Mate...always time to look these things over. If you're scheme registered you can always run it by them too.

 

[claret73]

Spin London...where does it say you can ignore Bonding??? Regardless of RCD or not?...Sorry I might have missed something?

 

[goldie]

Yes where PME conditions apply, both the earthing conductor and the protective bonding conductors have to be a minimum of 10mm².
However, bonding is not required for ADS or for RCDs to operate, as such there is no requirement to upgrade the bonding.

understood but before i do certain works on an existing installation i have to make sure certain aspects of the installation is up to current standards i.e main protective bonding and mentioned rcds because any cable i install will have to be protected by rcd (unskilled persons and cables buried less than 50mm)